Pneumatically actuated flexible coupling end effectors for lapping/polishing

ABSTRACT

Methods and apparatus for end effectors for performing surface lapping using a robotic system are provided. In one embodiment, a lapping system includes a robotic arm and a pneumatic end effector unit. The pneumatic end effector unit includes a first base attached to the robotic arm, a second base, a lapping pad attachable to the second base, and a pneumatic piston system coupled between the first and second bases. An abrasive pad is attached to the lapping pad with a layer of pitch. The pneumatic piston system includes a piston chamber, a piston being slideably received within the piston chamber, and a component for controlling air pressure within the piston chamber. A slurry system introduces a slurry compound into one of the second base or the lapping pad.

GOVERNMENT LICENSE RIGHTS

This invention was made with Government support under U.S. Governmentcontract F33615-97-2-3400 awarded by United States Air Force. TheGovernment has certain rights in this invention.

RELATED APPLICATIONS

This patent application is related to copending, commonly-owned patentapplications entitled “Contour Following End Effectors ForLapping/Polishing” U.S. patent application Ser. No. 10/301,999, filedNov. 21, 2002, “Spring-Loaded Contour Following End Effectors forLapping/Polishing”, U.S. patent application Ser. No. 10/302,042, filedNov. 21, 2002, and “Automated Lapping System”, U.S. patent applicationSer. No. 10/302,000, filed Nov. 21, 2002, which are hereby incorporatedby reference.

FIELD OF THE INVENTION

This invention relates generally to lapping and polishing surfaces and,more specifically, to robotic lapping and polishing.

BACKGROUND OF THE INVENTION

Injection-molded aircraft canopies and windshields offer tremendousbenefits to aircraft in cost, weight, and impact tolerance. A major costin this manufacturing process is the injection mold itself. Surfaces ofcanopies and windshields are finished to a quality similar to an opticlens in order to prevent pilots from being subjected to visualdistortion.

The precise optics for canopies and windshields are built into theinjection mold. The injection molds are lapped or polished by hand,section by section, using a diamond plated lapping material. Handpolishing or lapping an injection mold takes several man-years toaccomplish. Thus, lapping or polishing is very costly. Hand polishing orlapping also does not always ensure that the precise, optic surfacefinish quality has been met.

Therefore, there exists an unmet need to reduce the cost and increasethe accuracy of lapping or polishing.

SUMMARY OF THE INVENTION

The present invention provides end effectors for performing surfacelapping using a robotic system. The robotic system includes a roboticarm and a pneumatic end effector unit. The pneumatic end effector unitincludes a first base attached to the robotic arm, a second base, alapping pad attachable to the second base, and a pneumatic piston systemcoupled between the first and second bases. An abrasive pad is attachedto the lapping pad with a layer of pitch.

In one aspect of the invention, the pneumatic piston system includes apiston chamber, a piston being slideably received within the pistonchamber, and a component for controlling air pressure within the pistonchamber.

In another aspect of the invention, the piston chamber slideably guidesthe second base.

In still another aspect of the invention, the second base includes alatch that attaches the lapping pad to the second base.

In a further aspect of the invention, a slurry system introduces aslurry compound into one of the second base or the lapping pad.

BRIEF DESCRIPTION OF THE DRAWINGS

The preferred and alternative embodiments of the present invention aredescribed in detail below with reference to the following drawings.

FIG. 1 is a perspective view of an end effector in operation inaccordance with an embodiment of the invention;

FIG. 2 illustrates a perspective view of an exemplary pneumatic endeffector in accordance with an embodiment of the invention;

FIG. 3 is a cross-sectional view of the pneumatic end effector shown inFIG. 2;

FIG. 4 is an exploded view of exemplary materials layered on an endeffector;

FIGS. 5A–C illustrate perspective and plan views of the end effectorshown in FIG. 2;

FIGS. 6A and B illustrate side views of the end effector shown in FIG.2.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to apparatus and methods for providing endeffectors for performing surface lapping using a robotic system. Manyspecific details of certain embodiments of the invention are set forthin the following description and in FIGS. 1–6 to provide a thoroughunderstanding of such embodiments. One skilled in the art, however, willunderstand that the present invention may have additional embodiments,or that the present invention may be practiced without several of thedetails described in the following description.

FIG. 1 shows an embodiment of an end effector 30 in accordance with anembodiment of the present invention that is attached to a robot 20 forpolishing and lapping a work product 32. A non-limiting example of theproduct 32 is a core or cavity injection mold for making polycarbonateaircraft canopies. The work product 32 suitably entails a high degree ofpolishing or lapping accuracy. For example, precise optical propertiesfor injection molds must be attained in order to produce opticallyflawless or near-flawless polycarbonate molded canopies. In order toattain this desired level of accuracy, the end effector 30 pivots at anend of the robot 20, but does not rotate about an axis that isperpendicular to a planar surface of the end effector 30. In otherwords, the end effector 30 maintains a substantially orthogonal positionrelative to the work product 32.

A non-limiting example of the robot 20 includes a Fanuc, Inc. robot withsoft float. Soft float allows the robot 20 to apply pressure to asurface without resulting in undesired shut-offs. Because the robot 20applies continuous, consistent pressure that far exceeds thecapabilities of a human operator, lapping and polishing evolutions takea fraction of the time taken by a human operator.

FIG. 2 illustrates a perspective view of an exemplary pneumatic endeffector 30 in accordance with an embodiment of the invention.

FIGS. 3 and 4 illustrate cross-sectional and exploded views,respectively, of the end effector 30 of FIG. 2. As shown in FIG. 3, inone embodiment, the end effector 30 receives compressed air through anair logic controller 34 as controlled by a proportional integralderivative (PID) controller 36. The air logic controller 34 receiveshigh pressure air from a source. The air logic controller 34 providesconstant pressure between the end effector flexible coupling member 50and the work product 32. The PID controller 36 includes a control knobto increase or decrease the air pressure variably by turning the knob.The air logic controller 34 displays a digital readout of the airpressure commanded by the control knob of the PID controller 36 andsenses the pressure through the pneumatic tube 70. The sensed pressureis constantly monitored by the PID controller 36. The PID controller 36compensates for pressure variations by dispensing more or less airpressure through the air logic controller 34 as required to maintainconstant pressure at the end effector plate 50.

As further shown in FIGS. 2–4, in this embodiment, the end effector 30includes a first mounting plate 40, a piston cylinder 42, a piston 44, asecond mounting plate 48, and a flexible coupling member 50. In oneparticular embodiment, the flexible coupling member 50 includes across-slotted cylinder that acts as a flexible coupling between thesecond plate 48 and the abrasive lapping medium. The flexible couplingmember 50 may be fabricated out of any suitable semi-rigid material. Asdescribed more fully below, the end effector 30 having the flexiblecoupling member 50 may provide significant advantages over the priorart.

As shown in FIG. 4, the piston cylinder 42 includes a piston cavity 68that receives the piston 44. An O-ring 76 is positioned around thepiston 44 in order to come in contact with the walls of the pistoncavity 68 and the piston 44. The second mounting plate 48 includesbushings 64, such as polymer bushings, that are mounted withinthrough-holes of the second mounting plate 48. Guideposts 52 aresecurely received by the piston cylinder 42. The bushings 64 slideablyreceive the guideposts 52. The second mounting plate 48 is attached tothe piston 44 by a plurality of bolts 66 (FIG. 4).

As best shown in FIG. 4, attached to a lapping end or side of theflexible coupling member 50 is an adhesively bonded polymer bumper 58for damage control in the event of an abrasive media disbond, flexibleadhesive media 90 such as polysulphide or silicone, a layer of pitch 92,and a lapping abrasive 94, such as diamond media plated on a flexiblecloth gridwork.

The first mounting plate 40 includes a cavity 72 (FIG. 3) thatcommunicates at one end with the piston cavity 68, and at a second endreceives a pneumatic tube 70 that is coupled to the air logic controller34. Similarly, the second mounting plate 48 includes a slurry cavity 88that is open at one end to a slurry cavity 82 within the flexiblecoupling member 50. A second opening of the slurry cavity 88 receives aslurry tube 80 that receives an abrasive/polishing slurry from a slurrysystem 96. In one embodiment, the slurry system 96 is coupled to acomputer controller, such as described in copending patent applicationAutomated Lapping System.

FIGS. 5A–C illustrate perspective and plan views of an embodiment of alatch mechanism 110 that attaches the end effector flexible couplingmember 50 to the second mounting plate 48 and thus the piston 44. Thelatch mechanism 110 includes two halves that are rotatably attached viabolts 116 to a side of the second mounting plate 48 that is opposite theside that is in contact with the piston 44. Each of the halves includecoupling gears (FIG. 5B) that cause one of the halves to be activated ifthe other half is activated. Each of the halves include protruding pins113 (FIG. 4) that pass through holes in the second mounting plate 48into a spring cavity 111 that includes a spring 112 (FIGS. 4 and 5C).The spring 112 provides a contracting force on the protruding pins 113that forces the halves of the latch mechanism 110 into a closedposition. The base of the second mounting plate 48 includes a recessedarea 118 (FIG. 5A) between the two halves of the latch mechanism 110.The recessed area 118 includes a chocking pin 114. The flexible couplingmember 50 includes an external groove 130 and a chocking pin receivinghole 132 (FIG. 4). The flexible coupling member 50 is coupled to thesecond mounting plate 48 by opening up the latch mechanism 110,inserting the flexible coupling member 50 into the recessed area 118, sothat the chocking pin 114 is received by the chocking pin hole 132.Then, the latch mechanism 110 is placed in a closed position wherebyportions of each half of the latch mechanism 110 are received within thegroove 130.

FIG. 6A illustrates a side view of the end effector 30 when the piston44 is in a non-compressed or partially compressed position. In thenon-compressed position the piston 44 extends from the piston cylinder42 with the second mounting plate 48 being guided by the guide posts 52.FIG. 6B illustrates a side view of the end effector 30 when the piston44 is in a fully compressed position. In the fully compressed position,the piston 44 is fully received within the piston cylinder 42. Thesecond mounting plate 48 makes contact (or near contact) with the pistoncylinder 42 as guided by the guide posts 52.

In operation, the end effector 30 may be positioned proximate the workproduct 32 by the robot 20 such that the lapping abrasive 94 is engagedagainst a portion of the work product 32 that is to be polished. As thelapping abrasive 94 engages against the work product 32, a pressurewithin the piston cavity 68 is controlled via the pneumatic tube 70 bythe air logic controller 34 so that the lapping abrasive 94 is appliedwith a variably adjustable constant force against the work product 32. Aflow of abrasive slurry may enter the slurry cavity 82 via the slurrytube 80 from the slurry supply system 96, and may flow onto the workproduct 32 to facilitate the polishing process.

It will be appreciated that the end effector 30 having the flexiblecoupling member 50 provides a semi-rigid or flexible coupling betweenthe lapping abrasive 94 and the second plate 48. Thus, the flexiblecoupling member 50 may flex under pressure to allow the lapping abrasive94 to at least partially conform to the surface of the work piece 32.

Embodiments of apparatus and methods in accordance with the presentinvention may provide significant advantages over the prior art. Forexample, because the end effector 30 includes the flexible couplingmember 50 that maintains a semi-rigid state suitable for driving thelapping abrasive 94, yet still allows a degree of flexure between theend effector 30 and the work product 32. Thus, unlike alternatepolishing systems that assure normality of the lapping head to the workproduct 32, the end effector 30 in accordance with the present inventionallows the lapping abrasive 94 to conform to the surface of the workproduct 32.

Furthermore, because the end effector 30 includes a pneumatic piston 44,the force with which the lapping abrasive 94 is applied to the workproduct 32 may be adjustably controlled to a desired operating pressurethat remains constant as the lapping abrasive 94 is applied over variousportions of the work product 32. Thus, the polishing of the work product32 may be performed in a controllable, automated manner, and may therebyimprove the quality and reduce the costs associated with the polishingprocess.

While preferred and alternate embodiments of the invention have beenillustrated and described, as noted above, many changes can be madewithout departing from the spirit and scope of the invention.Accordingly, the scope of the invention is not limited by the disclosureof these preferred and alternate embodiments. Instead, the inventionshould be determined entirely by reference to the claims that follow.

1. A system for lapping a surface, the system comprising: a robotic arm;and a pneumatic end effector unit, wherein the pneumatic end effectorunit comprises: a first base attached to the robotic arm; a second base;a lapping medium attachable to the second base; a bumper coupled to thelapping medium; and a pneumatic piston system coupled between the firstand second bases.
 2. The system of claim 1, wherein the lapping mediumcomprises an abrasive member adapted to engage the surface.
 3. Thesystem of claim 1, further comprising: an abrasive pad; and a pitch forattaching the abrasive pad to the lapping medium.
 4. The system of claim1, wherein the pneumatic piston system comprises: a piston chamber; apiston being slideably received within the piston chamber; and acomponent for controlling air pressure within the piston chamber.
 5. Thesystem of claim 4, wherein the piston chamber is configured to guide thesecond base.
 6. The system of claim 1, wherein the second base comprisesa latch for attaching the lapping medium to the second base.
 7. Thesystem of claim 1, further comprising a slurry system coupled to one ofthe second base or the lapping medium for introducing a slurry compound.8. A lapping end effector, comprising: a first base attachable to arobotic arm; a second base; a flexible coupling member attachable to thesecond base; a bumper coupled to the flexible coupling member; and apneumatic piston system coupled between the first and second bases. 9.The end effector of claim 8, further comprising: a flexible couplingmember coupled between the lapping medium and the second base.
 10. Theend effector of claim 8, further comprising: an abrasive pad; and apitch for attaching the abrasive pad to the lapping medium.
 11. The endeffector of claim 8, wherein the pneumatic piston system comprises: apiston chamber; a piston being slideably received within the pistonchamber; and a component for controlling air pressure within the pistonchamber.
 12. The end effector of claim 11, wherein the piston chamber isconfigured to guide the second base.
 13. The end effector of claim 8,wherein the second base comprises a latch for attaching the lappingmedium to the second base.
 14. The end effector of claim 8, furthercomprising a slurry system coupled to one of the second base or thelapping medium for introducing a slurry compound.
 15. A lapping endeffector for performing an operation on a surface of a workpiece,comprising: a first base attachable to a robotic arm; a second baseattached to the first base; a lapping medium attached to the secondbase; and a flexible coupling system coupled between the lapping mediumand the second bases, the flexible coupling system configured to flex toallow the lapping medium to at least partially conform to the surface ofthe workpiece such that an axis of rotation of the lapping medium isnon-normal to the surface during performance of the operation.
 16. Theend effector of claim 15, wherein the first and second bases are coupledby a pneumatic piston system comprising: a piston chamber; a pistonbeing slideably received within the piston chamber; and a component forcontrolling air pressure within the piston chamber.
 17. The end effectorof claim 15, wherein the second base comprises a latch for attaching thelapping medium to the second base.